Liquefaction becomes a reality

The focus of Christchurch civic leaders remains largely fixed on the inner city and the many photo opportunities but many residents remain without water and only have intermittent power.

Worst affected are residents in the Avonside Drive/River Road area along the Avon River close to the centre of the city and in coastal suburbs like New Brighton, Bexley and Kaiapoi.

These residents have been told they may not get piped water again for weeks.

Emergency supplies and above-ground piping is being supplied to some, allowing them to use toilets again, although sewerage is being discharged into the Avon.

Anywhere near a waterway, swamp or old creek has been particularly badly affected by liquefaction and subsidence.

Liquefaction became evident immediately the quake stopped shaking on Saturday morning at 4.30. Many residents checking the outside of their homes in the eerily quiet aftermath would have heard the sound of water running.

For hours afterward it was assumed that water mains had burst because water bubbled up through crack in concrete like springs. But it brought black silty soil with it that covered driveways. When wet it had the consistency of heavy jelly.

In some cases small truckloads were deposited out the front of homes, raising concerns about whether there will be more slumping. When the silt dries it turns almost white and blows away in the breeze causing dust clouds.

Where the water and silt was trapped under concrete, paths and roads were pushed upward, tilting and breaking homes and creating mounds on roads and paths. The tar seal crust on many of these roads is now breaking up into rubble.

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16 Comments & Questions

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Where were the geotech reports that the council approved when they authorised building homes on this type of land?
And what about all the housing built over peat bogs in the south of Auckland? Would those homes collapse into the water tables if there were to be similar earthquakes ?

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The real issue is the fact the Council opposed these developments, but were defeated by greedy developers who threw their bottomless wallets at the Environment Court in opposing Council

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The tragedy for these people is that their homes will forever be tainted with the fact that this happened.

Even if they rebuild when a potential buyer sees the area or gets a LIM report from now on they will always be reminded of the quake risk.

So even though insurance may rebuild/repair the houses these people have lost an awful lot of equity which they will probably/perhaps never regain

A brick buildng in Town may be demolished and replaced and the owner is back where he started - maybe better off in a lot of cases - but these people in Avonside/Shirley/Kaiapoi have a grim financial reality to look forward to somewhere down the track when they wish to move on.

So I agree Anonymous really Council has something to answer for - especially in regards more recently built residence where the overzealous inspectors and planning people that seem to have abounded in recent years no doubt made the have the owner's lives a misery in the building process.

Perhaps a class action in the offing for the CCC?

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We visited Pegasus Town today where a number of our Kaiapoi neighbours have gone to stay with friends and we were amazed to find that there has been absolutely no damage whatsoever. Apparently the developer modelled a 7.2 magnitude quake with an epicentre 10km's from Pegasus as part of the liquefaction mitigation design. My wife said all the young mums at the play park were saying how lucky they are to not be having to worry about tremors and living in a totally safe place and able to use the drinking fountains and the public loos.

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This smells a bit of marketing by Pega-suss town.....

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No - you are wrong. This was not marketing from Pegasus Town. You may be interested in one of the many emails Pegasus received from residents in the first few days after the earthquake which is quoted here:
"Thank you, thank you. This place is amazing. We have family (as do many other residents here) from Christchurch who cannot get back into their homes and are staying with us. Going back to help them get the contents of their house, when they can, only emphaises why we want to live here. The residents (especially young mums) have been meeting by the playground with their young children and everyone is very glad to be here. Other new housing areas have had a lot of damage and Pegasus is on similar land with no damage which suggests Pegasus has been very well engineered." - Christine Johnston, Pegasus resident. (Posted with permission).

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Proper design undoubtedly saved Pegasus Town. I was contracted to do the ground improvements in that area. I am glad to read everyone is alright. Perhaps vibro-compaction should be considered in all sandy areas, like they have done in Dubai.

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Is insufficient liquefaction mitigation design going to be the next 'leaky building syndrome'?

Will the rebuilt houses be re engineered to cope with this in the future (at cost to insurer or insured?)

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Pegasus Town, wHAT A LOAD OF CRAP. Stop marketing your sh*t on here fagg*ots

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What a shame you despise the truth.
Your contribution is a disgrace.

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You are an idiot of biblical proportions Pegasus is the only development that 'got it right' 20 million on ground stabilisation paid off and no i dont work for Pegasus I just know that the bar has now been set for future developments by infinity go back to your can of woodstock you loser

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Liquefaction is mentioned on LIM already, the thing is most people have absolutely no idea what it is or how destructive. I live in Christchurch and have always been well aware that the biggest threat to Christchurch was liquefaction during an earthquake.

There are whole suburbs that are lucky to still be above sea level.

If anyone whats to see a small scale example of liquefaction go watch concrete being poured and the effect that that the application of the vibrator has, it is exactly the same. All the heavy objects (the stones) fall through the lighter sediment and the water comes to the surface carrying light sediment with it.

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Environment Catnerbury have had detailed reports on risks to certain areas for a while... Interesting to see the risks in Kaipoi reported over 100 years ago.

http://ecan.govt.nz/publications/General/solid-facts-christchurch-liquef...

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We live in Avonside Drive on the actual River and very close to Bracken street - My other main concern apart from our house being 1ft off the foundations and all wonkey - is the road immediatley outside our house - by the River the road has the most enormous fault line that is getting bigger with the constant trucks and flow of traffic - I look at it each day and see changes, puddles appearing in the road surface (movement) when cars speed by or heavy vehicles pass the house moves! - No one has placed an official SLOW sign, or ever shut the road off....I have made my own SLOW sign...what I am interested in kowing is what damage to that road is being done and what could be the consequences of our house moving more if that road completely fades in?

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No wonder Pegasus did not have the damage that Christchurch and Kaiapoi had. It's twice the distance from the epicentre as Chch and 1/2 again from Kaiapoi. Maybe Woodend should brag how well engineered it is!? And is the soil exactly the same?

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Again the urban myth was that pegasus would sink into the sea... well smell the coffee Woodend is not the same strata as Pegasus Pegasus was wetlands with a extreme liquifaction occurrance the same as Kaiapoi the shake was felt very strongly at Pegasus but the results speak for themselves

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